Treaties of Locarno, a series of seven international agreements drawn up at Locarno, Switzerland, and signed in London in 1925. The treaties were designed to preserve the existing French-German and Belgian-German borders, and to foster international cooperation to avoid war.
Austen Chamberlain of Great Britain, Aristide Briand of France, and Gustav Stresemann of Germany began negotiations in the summer of 1925 in an effort to reduce tensions in Europe arising from the Treaty of Versailles (1919). Talks continued through the autumn, and the treaties were signed in December.
The most important treaty was the Rhineland Security Compact, which provided for maintaining a demilitarized zone in the Rhineland section of Germany. Under this compact, Germany and France, and Germany and Belgium, agreed not to “attack or invade each other or resort to war against each other,” but supplementary clauses justified the use of force in self-defense. 
Britain and Italy pledged their aid to the victim in the event of a frontier violation. This clause was particularly welcomed by the French, since it meant the other countries would be obliged to come to France's assistance should Germany invade France.
The remaining six Locarno treaties pledged the participating nations to the peaceful settlement of international disputes and set up rules by which the arbitration of disputes was to be carried out. Germany agreed to respect these rules with regard to France, Belgium, Poland, and Czechoslovakia. France agreed to come to the aid of Poland and Czechoslovakia should Germany violate its pledges to these nations.
It was hoped that the conference would be an important step toward permanent peace in Europe. However, Germany sought to remilitarize the Rhineland after Adolf Hitler came to power in 1933. In 1936 Hitler sent German forces into the Rhineland and denounced the Locarno treaties. Britain and France lodged formal protests against Germany's action, but they did nothing to counter it.

Source: http://history.howstuffworks.com